Diagnostic assays are widespread and central for the diagnosis, treatment and management of many diseases. Different types of diagnostic assays have been developed over the years in order to simplify the detection of various analytes in clinical samples such as blood, serum, plasma, urine, saliva, tissue biopsies, stool, sputum, and skin or throat swabs. These assays are frequently expected to give a fast and reliable result, while being easy to use and cheap to manufacture. Understandably it is difficult to meet all these requirements in one and the same assay. In practice, many assays are limited by their speed. Another important parameter is sensitivity. Recent developments in assay technology have led to increasingly more sensitive tests that allow detection of an analyte in trace quantities as well the detection of disease indicators in a sample at the earliest time possible.
A common type of disposable assay device includes a zone or area for receiving the liquid sample, a capture zone, and optionally a transport or incubation zone connecting the receiving and capture zone, respectively. These assay devices are commonly known as lateral flow test strips. They employ a porous material, e.g., nitrocellulose, defining a path for fluid flow capable of supporting capillary flow. Examples include those shown in U.S. Pat. Nos. 5,559,041, 5,714,389, 5,120,643, and 6,228,660 all of which are incorporated herein by reference in their entireties.
The sample-receiving zone frequently consists of a more porous material, capable of absorbing the sample, and, when separation of blood cells is desired, also effective to trap the red blood cells. Examples of such materials are fibrous materials, such as paper, fleece, gel or tissue, comprising e.g. cellulose, wool, glass fiber, asbestos, synthetic fibers, polymers, or mixtures of the same.
Another type of assay devices is a non-porous assay having projections to induce capillary flow. A non-porous assay device is shown in FIG. 1. Examples of such assay devices include the open lateral flow device as disclosed in WO 03/103835, WO 2005/089082, WO 2005/118139, and WO 2006/137785, all of which are incorporated herein by reference in their entireties.
U.S. Pat. No. 6,156,273 discloses separation columns that include collocated monolith support structures and interconnected channels defined by the support structures.
In known assay devices having projections with round cross-sections, there are several problems associated with such round-cross sections. One drawback is the relatively large stagnation area in the front and the back of the projection, which is believed to contribute to spikes in signal due to trapped analyte conjugated with label and poor washing. Another drawback is the relatively large background signal generated by the geometry of the round projection. Yet another drawback is the thick depletion layer with a symmetric round pillar arrangement, which slows the capture of the labeled analyte, leading to decreased sensitivity.
Accordingly, there is a need for further improved kinetics, increased sensitivity and specificity in methods and devices for biochemical and biomolecular assays, in particular for diagnostic assays where the requirements for sensitivity and accuracy are very high. In particular, there is a need for a projection geometry that can minimize background signal with a thin depletion layer and minimized stagnation regions surrounding the projections.